Computer printers normally operate by drawing single sheets of blank media (such as paper or transparent film) from a horizontal stack of sheets. Each sheet is individually drawn or “picked” from the stack and fed into the media path of the printer. If no sheets are drawn during an attempted pick, a “no pick” failure has occurred; if two (or more) sheets are picked in an overlapping manner, a “two (or multiple) pick” failure has occurred. If the sheets are not properly aligned and properly located at the designated picking location, the aforementioned failures can occur plus the sheets may jam in the media path or the print on the sheets may be skewed. In the event of any of these failures, printing may be suspended, media may be wasted, and a user may be inconvenienced.
Some printers have attempted to solve the problem of media not being aligned at the proper picking location by using a removable media tray with teeth on an inside wall of the tray, which provide a media stop. But, this technique requires extra parts, which increases the cost of the printer. Also, the user is inconvenienced by having to remove the media tray in order to replenish the media.
Although the above discussion has described the problems associated with feeding media through a printer, the problems apply equally to other types of devices that feed media, such as copiers, fax machines, scanners, plotters, currency counters, and ATMs (Automated Teller Machines).